Continuous production and separation of carbon-based materials

ABSTRACT

The invention relates to several apparatuses and methods for the continuous production of carbon soot with a high content of fullerenes, endohedral metallofullerenes (EMFs), and carbon nanotubes. In addition, the invention relates to anaerobic manipulations of carbon-based compounds. The claimed apparatuses and methods provide optimal conditions during annealing processes. In particular, the rotary shielding block of the present invention can effectively prevent resultant products from exposure to intense ultraviolet radiation associated with vaporization processes.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a non-provisional application claimingpriority to provisional application Serial No. 60/418,964 filed Oct. 16,2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an apparatus and a process foroptimized annealing during graphite vaporization wherein exposure tointense ultraviolet radiation is minimized. The invention provides massproduction methods for fullerenes, endohedral metallofullerenes (EMFs)and other carbon-based materials through effective shielding fromdestructive UV radiation during graphite vaporization. This provides forslower cooling of the annealed carbon compounds and increased yields ofup to 10 times or even better over conventional production techniques.

[0004] 2. Description of the Prior Art

[0005] In 1985, the unique stability of molecular allotropic forms suchas C₆₀ and C₇₀ was demonstrated [H. W. Kroto et al.; Nature 318, 162(1985)]. This event led to the discovery of a whole new set ofcarbon-based substances known as fullerenes. The configuration of carbonatoms in fullerenes provides unique properties that have captured theinterest of chemists, physicists, materials scientists, and medicalresearchers, as fullerenes have been shown to crystallize to forminteresting solids and to polymerize in several ways to form newpolymers. Fullerene compounds can be reacted with other chemicals in anumber of ways to form new molecules of interest. Tubules of fullerenes,known as carbon nanotubes, have caught increasing interest as fibers,nanowires, and encapsulants. Fullerenes can also be doped to formelectronic materials or reacted to form superconductors.

[0006] All of these applications have been discovered since the firstmacroscopic amounts of the most common two fullerenes, C₆₀ and C₇₀, wereisolated in 1990 [Krätschmer, et al., Nature 347, 354 (1990)]. Much ofthe work on fullerenes is performed using small amounts of material, assynthetic production of these forms of carbon yielded limited quantitiesof material. The major drawback to the commercialization of some of theapplications mentioned has been the lack of a large-scaled method forproducing and isolating fullerenes.

[0007] Synthetic production of fullerenes was first provided usingvaporization of graphite in an expanding helium atmosphere [H. W. Kroto,et al., Nature 318, 162 (1985)]. In this method, a Q-switched Nd:YAGlaser is focused onto a rotating disc of graphite, whereupon carbon isevaporated or ablated into a high-density helium flow. Clusters of sootform and are detected using a time-of-flight mass spectrometer. However,this method of production is sufficient to form only a few micrograms offullerenes per day, which is only enough for certain, limited researchpurposes.

[0008] A more useful method of synthesizing fullerene-containing soot isthe electric-arc method [Krätschmer, et al., Nature 347, 354 (1990)]. Ina variation of this method known as the contact arc process, lightlycontacting graphite electrodes are heated electrically by anelectric-arc welder in an atmosphere of helium at a pressure of about 50to about 300 torr. The porous graphite electrodes are vaporized by thearc welder to produce soot containing fullerenes. The soot condensesupon cool walls of a chamber, and is scraped off after the electrodesare consumed. Fullerenes are then extracted from the soot by a solvent,such as toluene, carbon disulfite, toluene, or benzene. This method iscapable of producing a few tens of milligrams of fullerenes per run. Byrunning several arc welders in parallel, the process is capable ofproducing several grams of fullerenes per day. The process isencumbered, however, with scaling problems. For example, as the diameterof the rods gets bigger and the current supplied to the rods gets higherto increase the amount of graphite evaporated per unit of time, theyield of fullerenes decreases. Although the linear decrease in yieldwith an increase in rod diameter and with a decrease in the anglebetween the two electrodes is not understood, a reasonable conjectureput forth by Chibante, et al. [(J. Phys. Chem. 97(34), 8696 (1993)], isthat the intense ultraviolet light in the plasma region of the arc maydestroy fullerenes before they can exit that region.

[0009] Howard, et al. in Nature 352,139 (1991) discloses a third methodof producing fullerenes. This method entails burning hydrocarbon feedsin an oxygen deficient flame or sooty flame. Benzene is used as ahydrocarbon source, with an argon diluted oxygen supply. In this method,it was found that soot yields are 0.2 to 12% of the carbon feed, givinga maximum yield of fullerenes of 0.3% of the carbon feed. This synthesisprocess has been improved by scientists at TDA Inc., but the process cannot be applied to the production of EMFs because metal precursors cannot be delivered into the carbon annealing zone.

[0010] Chibante et al, in J. Phys. Chem. 97(34), 8696 (1993) andLaplaze, et al, in Syn. Metals 86, 2295 (1997) and others, show a fourthmethod of production using solar radiation. These small scaleexperiments, using a 2 kW solar furnace, have shown that efficiencies ofup to 20% can be reached. However, there is an inherent problemassociated with using a solar furnace—the small solar furnace has a weakfocus area and larger furnaces require more area to collect solarradiation. Chibante et al, in J. Phys. Chem. 97(34), 8696 (1993) studiedmany other useful experimental parameters on various graphitevaporization techniques, as mentioned earlier. The limitation of thevaporized graphite rod, the angle between the electrode, and temperaturedependence of the vaporization have been investigated carefully. Asmentioned, shielding of the destructive and intense radiation duringvaporization is a novel advance in the production of fullerenes andrelated carbonaceous compounds.

[0011] The prior art methods of producing fullerenes, namely, laserablation of graphite targets, the electric-arc process, the solarpreparation, and the process whereby soot produced by an oxygendeficient flame is utilized, are encumbered by small productioncapacities, producing at most only milligram quantities of fillerenes,loss of efficiency as the electrode diameter is increased, and the highexpense, low yields of soot from benzene. For these reasons, currentmethods of fullerene production are largely impractical. A moreeconomical and scalable method of fullerene production is needed.

SUMMARY OF THE INVENTION

[0012] First, the invention provides an apparatus and method forproducing fullerenes, EMFs, carbon nanotubes, and other carbon materialsin quantities greater than the few hundred milligrams produced per dayby the conventional techniques such as contact-arc, laser ablation, andsolar radiation vaporization.

[0013] Second, the invention provides a scalable method for continuouslyproducing fullerenes in greater quantities than the small amountsavailable through current methods, without losing efficiency inproduction from increases in the electrode diameters.

[0014] Third, the invention provides an apparatus and method foreffectively transferring fullerenes, EMFs, carbon nanotubes, and othercarbon materials from the destructive vaporization zone using theconstant flow of buffer gas.

[0015] Fourth, the invention provides a method or producing increasedamounts of fullerenes, EMFs and other carbonaceous compounds usinglonger annealing times by using a graphite guide tube, which can beheated by an arc plasma.

[0016] Fifth, the invention provides an apparatus and method forproducing increased amounts of fullerenes, EMFs and other carbonaceouscompounds under more optimal conditions for delivering metal precursors.

[0017] Sixth, the invention provides an apparatus and method forproducing increased amounts of fullerenes, EMFs and other carbonaceouscompounds by decreasing the exposure from destructive high energyradiation during vaporization by using a graphite guide tube and arotary shielding block.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0018]FIG. 1 shows a prior art apparatus with A) bisectional view of theconventional contact-arc reactor in prior art, and the differentarrangement of the contact-arc electrodes, B) 180 degree angle betweenthe rotary and linear motion graphite electrodes, and C) 90 degree anglebetween rotary and linear motion graphite electrodes.

[0019]FIG. 2 shows a block diagram of the present invention.

[0020]FIG. 3 shows a bisectional view of the apparatus with the graphiteshielding tube of the present invention.

[0021]FIG. 4 shows A) the detail of the bottom side, B) the connectionmode of the separated collector with a sublimator, and C) a sublimationprocess in a tube furnace.

[0022]FIG. 5 shows A) a Schlenk line collector and B) anaerobicmanipulation by using the cannular technique.

[0023]FIG. 6 shows a bisectional view of the apparatus with a heatreserving guide tube and a rotary graphite shielding block.

[0024]FIG. 7 shows A) a the bisectional view of the modified apparatusof FIG. 6 of which both electrodes are tilted 30 degrees from horizonand B) the position of two electrodes, which are perpendicular eachother, which are perpendicular each other, from top view.

[0025]FIG. 8 shows another block diagram of the present invention.

[0026]FIG. 9 shows a bisectional view of the apparatus with laser andsolar radiation sources.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Manufacturing fullerenes requires a source of small, gas phasecarbon clusters of from 2 to 10 atoms. Two sources of these carbonclusters exist. One is the disproportionation reaction in flame ofhydrocarbons or CO in an oxygen deficient flame to produce carbon soot.While the percentage of fullerenes in the soot may seem relatively high,the yield of fullerenes compared to the mass of hydrocarbon consumed islow. The other source is the vaporization of graphite at temperaturesabove 3000 degree C., whereupon the vaporized carbon is then condensedinto carbon soot. While this arc method has proven to be the mostuseful, even this method yields only tenths of grams of fullerenes perhour. None of the existing methods of production are capable of beingadapted for large-scale production.

[0028] The present invention provides an apparatus and a process foroptimized annealing during graphite vaporization wherein heat fromplasma carbon is directed into a limited area to provide a slowercooling process. The invention uses a shielding block and narrowed gasflow channels to rapidly move vaporized carbon from the area of intensedestructive radiation to a shielded condensation area. In addition, thegeometric arrangement of the shielding block can further reduce theexposure on products to destructive high-energy UV radiation duringvaporization. Under these conditions, yields are dramatically increasedand the apparatus can be scaled-up for mass production.

[0029]FIG. 1 shows a conventional electric-arc reactor that iswell-known in art. Rotary graphite electrodes (RGE) 20 andlinear-feeding porous graphite electrode (LFE) 30 are arranged for arccontact in a stainless steel, water-cooled, double-wall (SWD) chamber10.

[0030]FIG. 2 shows the block diagram of an electric-arc reactor of thepresent invention. The collector section can be separated withoutdisturbing the main system and allows continuous collections andanaerobic manipulation of the resultant product soot.

[0031]FIG. 3 shows another embodiment of the present invention. The mainchamber 10 is the SWC jacket, which has two O-rings or cupper gasketsealed flanges (OSFs or CGFs) attached at both ends or a quartz tubewith SWD installed OSF on both ends. After purging the reactor, constantinert gas (typically helium, nitrogen, argon) flow can be set up by amass flow controller (MFC). Then, electric current is applied to bothelectrodes (20 and 30), which are electrically insulated, while theconstant inert gas flows though inlet valve 35. Carbon clusters fromvaporized graphite travel with the inert gas flow. From the BernoulliTheorem, the flow rate increases when the vaporized soot passes nearfixed electrode 20, because of the narrower path. During thevaporization, the guide tube 60 will become heated. Middle chamber 70 isan SWD jacket with a stopper 75 where the vaporized soot is accumulated.During the vaporization process, monitoring of the thermal distributionis accomplished by using a CCD detector or the temperature on thespecific part of the reactor through the window 130 (FIGS. 7 and 9),which is not shown in FIG. 3. the change of electric properties, such asconductance, or resistance between two electrodes, can be monitored aswell. Final product will be transferred into the quartz collector 90 byopening the stopper 75 and wide-mouth, straight-through, metal or o-ringsealed valves, 80 and 82. After collecting all the carbon soot from thechamber, the stopper 75 is closed and several inert gas pulses aredirected into the chamber to collect soot from the wall. The stopper 75is then opened to collect the rest of the carbon soot. This process canbe repeated several times.

[0032]FIG. 4 shows the bottom part of the apparatus, which can producecarbon-based material in continuous mode. On the collector 90, anattached stopcock with schlenk connector 92 provides anaerobicmanipulation. The Schlenk line is used while valves 80 and 82 are keptclosed to keep pressure in the chamber and collector. After valve 82 isclosed, the collector 90 can be detached for removal of the carbonmaterials. An additional flange covers the bottom of the middle chamber70, and the valve 85 opens to the vacuum to evacuate all the air fromthe connection. During collection, an additional sublimator can beattached on top of the valve 82, and then valve 95 is opened to evacuateall the buffer gas from the sublimator. This cycle of purging andopening is then repeated. The sublimation system can be set up into atube furnace, and then the valve 82 is opened carefully. The sublimator97 inserts into the collector, running the cooling water in rod 93, as aheat exchange system, and then the system is purged until the pressuregoes down to 10⁻³ torr by using a secondary diffusion or other highperformance vacuum pump. The fraction collected in a certain temperaturerange gives specific fullerene molecules, as is well known in art.Repeated sublimations provide initial purification of fullerenes andEMFs. Before detaching sublimator with valve 82, if necessary,additional solvent extraction can be done in anaerobic conditions, asshown in FIG. 5.

[0033]FIG. 5 shows anaerobic manipulations by using Schlenk Techniques.The resultant soot can be transferred to other glassware by using acommon Schlenk technique, such as the cannular method. Then solventextraction can be performed for further separations. In addition, theresultant soot can be transferred without detaching collector 90 byusing the Schlenk Technique.

[0034]FIG. 6 shows another embodiment of the present invention. The mainchamber 10 will be the SWD jacket or quartz tube, as in FIG. 3. Thevaporization area surrounded by a main guide tube (MGT) 100 and a rotaryshielding block (RSB) 120 can reserve the heat from plasma and escapethe resultant product from the plasma area to minimize exposure highenergy UV radiation. The guide graphite tube 100 will be fixed by usinga water-cooled feed through valve 102. Inert gas flow rate through inletvalve 35 can be adjusted by using a MFC. Zirconia tube 33, or other hightemperature resistant material can be used or guide tube 60 can bedirectly attached on the wall in main chamber 10. The quartz tubechamber does not need electric insulation, but it needs an additionalair-cooling system around the chamber. The cartridge 36 can load severalporous graphite rods. After consuming the feeding electrode, a newporous graphite rod in 36 can be easily replaced without any difficulty.The cartridge 36 can be employed and modified in the bullet loadingsystem from the conventional automatic weapon and others easilyavailable in art. The RSB 120 can be rotated in various speeds withrotary feed-through and an additional scrapper directly attached on RSB120, if necessary. Rotation of the shield block creates a suctioneffect, thereby drawing the vaporized carbon particles downstream.Middle chamber 70 is a SWD jacket with a stopper 75 used foraccumulating vaporized soot. The collection process is the same asdescribed in connection with the description of FIG. 3.

[0035]FIG. 7 shows another variation of the apparatus of the presentinvention. As is well-known in the art, product yields vary according tothe position of the electrodes. This figure show only one position ofthe electrodes. In the present invention, the flow of inert gas givesthe effective escape of the resultant carbon soot by following theBernoulli Theorem. Also, the rotation speed of the shielding block 120is an additional factor in reducing the exposure of the product to UVradiation.

[0036]FIG. 8 shows a block diagram of the apparatus using laser or solarvaporization techniques. The vaporization energy source can be attachedto the top of the reactor with the stream of the inert gas flow. Inaddition, preheating the graphite element can raise the temperature upto 2000 degree C., and gives smoother vaporization and better yields.

[0037]FIG. 9 shows one type of the apparatus of the present inventiondeveloped from FIG. 8. Vaporization sources, such as a laser or a solarradiation collector system, is attached on the window 140. The positionof the focal point can be adjusted by using a reflecting system or bychanging the lens positions. Before starting vaporization, optionalpreheating system 152 can be used for smoother vaporization. Heatingsystem 152 is made of a graphite heating element found in commercialvacuum furnaces, which can heat up to 2000 degree C. The heatdistributions inside the main chamber can be monitored as mentioned inFIG. 3. The rotation speed of RSB 120 can be affected the efficiency ofthe production.

[0038] Carbon source materials for producing fullerenes can be selectedfrom among graphite, graphite powder, glassy carbon and amorphouscarbon; however, graphite is preferred. A porous graphite rod is alsopreferred because it has more surface area, including a hemisphericalcavity in its top surface. Also, it provides greater amounts of sootcontaining higher amounts of fullerenes. Moreover, it can be handledvery easily. Furthermore, the impregnation of the metal precursor in aporous graphite rod to prepare EMFs is well-known in the art.

[0039] In general, increased yields from the present invention areaccomplished by effective shielding and by directing heat from plasmacarbon into a limited area of the reactor during vaporization, and byquickly transporting vaporized graphite in flowing inert gas to keep theresultant product away from the destructive UV radiation area. Fullereneproduction yields are also affected by the:

[0040] a) length and diameter of the both end on main guide tube (MGT),

[0041] b) diameter of the both electrodes,

[0042] c) number of vaporized electrodes,

[0043] d) flow rate of inert gas,

[0044] e) mixed ratio of inert gas,

[0045] f) interval of the vaporization process,

[0046] g) rotation speed of the shielding block (in FIGS. 6 and 9),

[0047] h) geometry of the electrodes and number of electrodes (FIG. 6),

[0048] i) mixed ratio of inert gas, if necessary, (He, N₂, Ar, andothers)

[0049] j) preheating temperature for inert gas, and

[0050] k) energy source on vaporization.

[0051] In the present invention, EMFs can be produced by thevaporization of metal compound impregnated porous graphite rods andother metal containing carbon sources. Various metal impregnationprocesses on porous graphite rod are readily available from the priorart. For example, the soaking method [Cagle et al, JACS, 118, 8043(1996)] has been developed, and the content of the metal precursor onthe graphite rod can be controlled by the concentration of the metalcompound solution. Metal impregnated graphite rods can be purchased fromToyo Tanso, Co, in Japan. [Shinohara, et al, Bioconjugate Chem., 12, 510(2001)]

[0052] Table 1 shows some EMFs obtained from the present invention. Theprevious reported trimetallic nitride template (TNT) process [Dom, etal, Nature, 401, 6748 (1999); U.S. Pat. No. 6,303,760 (2001)] can alsobe easily adapted. Various metal compositions on graphite rod can becontrolled and can be easily investigated to reach optimal conditions ofEMF production. The present invention will expand the currentlyavailable EMF family to all transition metals and other metal elements,because of the optimal conditions for metal precursor delivery. Placingboron and nitrogen atoms into the cage structure is possible using borondoped graphite rod, and using partial pressure of nitrogen as a buffergas.

[0053] In prior art on EMF production, only minor variations onKrätschmer-Huffmann generator [Krätschmer, et al., Nature 347, 354(1990)] have been investigated. The present invention offers a majoroverhaul in the production of EMFs and higher fullerenes over 80 atomsin cage.

[0054] Table 1 the possible combination of EMFs between endohedralportion and fullerene cages Endohedrals Cage Remark M_(a) C_(2n) a =1-3, b = 0-2 M_(a) L_(b) K_(a − b − 3) C = 1-2 M_(a) N_(c) d = 1 orhigher, n = 30 or higher M_(a) L_(b) K_(a − b − 3)N_(c) M, L, K = metal;N = nitrogen

[0055] The foregoing description is illustrative only of the principalsof the invention. Further, since numerous modifications and changes willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed. Accordingly, all suitable modifications and equivalence maybe resorted to within the scope of the invention.

What is claimed is:
 1. Apparatus for manufacturing carbon compounds,comprising: a first electrode proximate a second electrode and defininga gap thereinbetween for producing carbon compounds; a first chamberextending around said gap and defining a first effective cross-sectionand a second effective cross-section, said second effectivecross-section being downstream of said first effective cross-section andhaving a size less than said first effective cross-section; a secondchamber in fluid communication with said first chamber; a gas inlet influid communication with said first chamber; and a gas entering throughsaid gas inlet, flowing through said first chamber and across said gap,said gas carrying the carbon compounds into said second chamber.
 2. Theapparatus of claim 1 wherein said first electrode comprises alinear-feeding porous graphite electrode and said second electrodecomprises a rotary graphite electrode.
 3. The apparatus of claim 2wherein said first electrode has a smaller cross-sectional area thansaid second electrode.
 4. The apparatus of claim 1 further comprising asoot accumulation chamber in fluid communication with said secondchamber.
 5. The apparatus of claim 4 further comprising a collectorapparatus connected to said soot accumulation chamber.
 6. The apparatusof claim 5 wherein said collector apparatus continuously collects thecarbon compounds.
 7. Apparatus for manufacturing carbon compounds,comprising: a first electrode proximate a second electrode and defininga gap thereinbetween for producing carbon compounds; a first chamberextending around said gap and defining a first effective cross-sectionand a second effective cross-section, said second effectivecross-section being downstream of said first effective cross-section andhaving a size less than said first effective cross-section; a secondchamber in fluid communication with said first chamber; a gas inlet influid communication with said first chamber; a shield; and a gasentering through said gas inlet, flowing through said first chamber andacross said gap, said gas carrying the carbon compounds past said shieldinto said second chamber.
 8. The apparatus of claim 7 wherein said firstelectrode comprises a linear-feeding porous graphite electrode and saidsecond electrode comprises a rotary graphite electrode.
 9. The apparatusof claim 8 wherein said first electrode has a smaller cross-sectionalarea than said second electrode.
 10. The apparatus of claim 7 furthercomprising a soot accumulation chamber in fluid communication with saidsecond chamber.
 11. The apparatus of claim 10 further comprising acollector apparatus connected to said soot accumulation chamber.
 12. Theapparatus of claim 11 wherein said collector apparatus continuouslycollects the carbon compounds.
 13. The apparatus of claim 7 wherein saidshield defines said first chamber.
 14. The apparatus of claim 7 whereinsaid shield rotates.
 15. The apparatus of claim 14 further comprisingmeans for scraping accumulated carbon compounds from said shield. 16.Apparatus for manufacturing carbon compounds, comprising: a firstchamber in fluid communication with a second chamber; a vaporizationlocation within said first chamber; means for producing carbon plasma atsaid vaporization location; means for directing a carrier gas from saidfirst chamber into said second chamber; means for increasing gas flowacross said vaporization location; means for shielding said vaporizationlocation from said second chamber.
 17. The apparatus of claim 16 whereinsaid means for producing carbon plasma comprises opposing first andsecond graphite electrodes defining a gap thereinbetween for producingcarbon compounds.
 18. The apparatus of claim 16 wherein said means forincreasing gas flow comprises a shield having a first effectivecross-section and a second effective cross-section, said secondeffective cross-section being downstream of said first effectivecross-section and having a size less than said first effectivecross-section;
 19. The apparatus of claim 16 wherein said means forshielding defines said first chamber.
 20. The apparatus of claim 16wherein said means for shielding comprises a rotating spheroid.
 21. Theapparatus of claim 16 wherein said apparatus is continuously operated.